1. Field of the Disclosure
Embodiments disclosed herein relate generally to a process for carbon dioxide sequestration for producing a liquid carbon dioxide stream, which may be used, for example, for enhanced oil recovery. More specifically, embodiments disclosed herein relate to a process for carbon dioxide purification integrating membrane technology, carbon dioxide distillation, and use of carbon dioxide as a self-refrigerant to result in an improved process capable of recovering a high percentage of carbon dioxide in the feed at a high purity.
2. Background
Various reservoir flooding techniques have been utilized by the oil and gas industry in enhanced oil recovery programs as a means to increase the production of hydrocarbons. In carbon dioxide flooding, carbon dioxide is pumped into the reservoir through an injection well for extended periods of time (e.g., years). The injected carbon dioxide “floods” the treated zone and forces/carries the oil in the formation toward one or more production wells where the fluids are recovered. The composition of the produced fluids changes with time and, at some point, carbon dioxide “breakthrough” will occur. After breakthrough the volume of gas and the carbon dioxide content of the produced fluids increase substantially.
Carbon dioxide may represent 60-96 mol percent (or more) of the fluids produced. In order for carbon dioxide flooding operations to be economically viable, carbon dioxide must be efficiently recovered from the produced fluids for reuse. In many cases, recovered carbon dioxide can be re-injected into the formation through the injection well, provided chemical specifications for purity are met. Product specifications for carbon dioxide can be quite high, particularly with respect to the content of hydrocarbons (i.e., methane and ethane) and/or nitrogen.
Carbon dioxide used in flooding operations may come from a variety of sources, including off-gases from chemical processes, among other sources. Processes to purify such carbon dioxide-rich streams typically involve removal of light gases such as hydrogen, nitrogen, oxygen, methane, and carbon monoxide. Many of these streams have low carbon dioxide content, including lime kiln gas, boiler flue gas and certain natural gases.
To recover carbon dioxide from streams having a low carbon dioxide content, such as a boiler flue gas stream, one solution is to scrub the gas mixture which is lean in carbon dioxide with a suitable solvent, such as monoethanolamine, sulfolane or potassium carbonate, to dissolve the carbon dioxide and then to strip the carbon dioxide from the solution so obtained; i.e., another fluid is introduced into the system in order to achieve the necessary separation. The carbon dioxide can then be compressed, dried, cooled and further purified by partial condensation or distillation. However this process is expensive in energy and a less energy-intensive alternative would be desirable.
Various other processes to recover and/or purify carbon dioxide are disclosed in U.S. Pat. Nos. 4,602,477, 4,639,257, 4,762,543, 4,936,887, 6,070,431, and 7,124,605, among others.
Large scale carbon dioxide processes are also discussed in: Hegerland et al., “Liquefaction and handling of large amount of CO2 for EOR,” Project Invest as, Norway, YARA International ASA (volume, date, etc.); Berger et al, “Creating a large scale CO2 infrastructure for enhanced oil recovery,” presented at the 7th International Conference of Greenhouse Gas Control Technologies, Vancouver, 2004; and in Song et al, SPE Formation Evaluation, Society of Petroleum Engineers, December 1987.
There remains a need for processes having improved carbon dioxide recovery while maintaining a high purity for the recovered carbon dioxide.